Abstract
Chromium(VI) (Cr(VI)) is the main chromium species found in groundwater and is considered as a highly toxic and carcinogenic element to humans. In the present study, removal of Cr(VI) by coagulation with ferrous iron is studied in a continuous flow treatment unit comprising pipe flocculation reactors followed by a sand filter. The studied parameters, regarding their effect on the removal of hexavalent chromium, were the ferrous iron dose, the effect of linear velocity, and the effect of the starting Cr(VI) concentration. The experiments have shown that the Cr(VI) removal achieved was very efficient and residual Cr(VI) and total Cr concentration in the treated water was lower than 10 μg/L, provided that the required dose of ferrous iron is provided. In particular, the study demonstrated that the removal of hexavalent chromium, from initial concentration of 50 μg/L and 100 μg/L, was more than 90% with ferrous doses of 1 mg/L and 2 mg/L respectively, applying linear velocity of 8 m/h, at an initial pH value of 7.3. Iron concentration in treated water was very low, far below 200 μg/L, which is the limit for iron in drinking water. This unit comprises a simple treatment option, for applications at the household level, with minimum maintenance requirements capable of removing Cr(VI) to concentrations below 10 μg/L, which might be the future limit for chromium in drinking water.
Highlights
The presence of chromium in natural and engineered aquatic systems is due to natural sources as well as to anthropogenic activities
The main objective of this research is to study the removal of hexavalent chromium from water by chemical reduction and precipitation using ferrous sulfate as the reducing agent followed by sand filtration, using an innovative treatment apparatus, which runs in full-scale mode and uses pipe reactors to promote the reaction of Fe(II) with Cr(VI)
The results of the present study showed that the examined experimental set up, compromising plug flow reactors followed by sand filtration, could achieve Cr(VI) removal rates of more than 90%
Summary
The presence of chromium in natural and engineered aquatic systems is due to natural sources as well as to anthropogenic activities. Natural sources of chromium are mainly rock disintegration [1,2], whereas anthropogenic activities that contribute to elevated chromium concentrations in water sources are mainly industrial activities, such as for example the electroplating industry, stainless steel production, leather tanning, and textile manufacturing [3]. Chromium is present in its two most stable oxidation states, namely, Cr(III), and Cr(VI). In chromium-containing natural water, the prevailing form is Cr(VI), because it is very soluble, whereas Cr(III) is quite insoluble, forming complexes with iron oxides or other minerals and, precipitating out of water [4].
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